Merge tag '0.4' into develop

0.4 (2018-02-18)
----------------

- Front: ambiant colors in player based on current track cover (#59)
- Front: simplified front dev setup thanks to webpack proxy (#59)
- Front: added some unittests for the store (#55)
- Front: fixed broken login redirection when 401
- Front: Removed autoplay on page reload
- API: Added a /instance/settings endpoint
- Front: load /instance/settings on page load
- Added settings to report JS and Python error to a Sentry instance
  This is disabled by default, but feel free to enable it if you want
  to help us by sending your error reports :) (#8)